Conventionally, in production of an organic EL element, a vapor deposition mask that is composed of a metal formed by a number of microscopic slits being arranged in parallel with one another at microscopic spaces in a region that should be subjected to vapor deposition, for example, has been used in formation of an organic layer of an organic EL element or a cathode electrode. While in the case of using the vapor deposition mask, the vapor deposition mask is placed on a substrate front surface that should be subjected to vapor deposition and is held by using a magnet from a back surface, the rigidity of the slits is extremely small, and therefore, distortion easily occurs to the slits when the vapor deposition mask is held on the substrate front surface, which becomes an obstacle to enhancement in definition or upsizing of the products in which the slit lengths are large.
Various studies have been made on the vapor deposition masks for preventing distortion of slits, and, for example, Patent Literature 1 proposes a vapor deposition mask including a base plate that also serves a first metal mask including a plurality of openings, a second metal mask including a number of microscopic slits in regions to cover the aforementioned openings, and a mask pulling and holding device that positions the second metal mask on the base plate in a state in which the second metal mask is pulled in the longitudinal direction of the slits. Namely, the vapor deposition mask with two kinds of metal masks being combined is proposed. It is indicated that according to the vapor deposition mask, slit precision can be ensured without occurrence of distortion to the slits.
Incidentally, in recent years, with upsizing of the products using organic EL elements or increase in substrate sizes, a demand for upsizing are also growing with respect to vapor deposition masks, and the metal plates for use in production of the vapor deposition masks composed of metals are also upsized. However, with the present metal processing technique, it is difficult to form slits in a large metal plate with high precision, and even if distortion in slit portions can be prevented by the method proposed in the above described Patent Literature 1 or the like, the method or the like cannot respond to enhancement in definition of the slits. Further, in the case of use of a vapor deposition mask composed of only a metal, the weight thereof also increases with upsizing, and the total mass including a frame also increases, which becomes a hindrance to handling.
Furthermore, while a vapor deposition mask is usually used in a state fixed to the frame, when the vapor deposition mask is upsized, there arises the problem of being incapable of performing positioning of the frame and the vapor deposition mask with high precision. In particular, in the case of a multiple-surface imposition vapor deposition mask configured by arranging a plurality of masks by dividing the plurality of masks in lengthwise and crosswise directions of the inside of the frame, displacement occurs to opening patterns of the respective masks unless positioning of the respective masks and the frame is performed with high precision, and therefore, the positioning precision problem becomes noticeable.
Further, in regard with a multiple-surface imposition vapor deposition mask, Patent Literature 2 proposes the configuration in which as the vapor deposition mask to be attached to the frame, a plurality of strip-shaped unit masks divided in the longitudinal direction of a frame opening (In the unit mask, a plurality of unit masking patterns are formed at predetermined spaces along the longitudinal direction thereof.) are used, and both end portions of the respective plurality of unit masks are fixed and attached to the frame in the short length direction of the frame opening so as to be given a predetermined pulling force. It is indicated that according to the configuration, even if the multiple-surface imposition vapor deposition mask (the opening area of the frame) is upsized, the positional displacements of the respective unit masking patterns due to distortion by the tare weight of the mask and the like can be restrained.
By using a plurality of strip-shaped unit masks as in Patent Literature 2, the positioning displacement in one direction (a short length direction) in the frame opening is certainly restrained to some degree, but unless positioning at the time of attaching the unit masks in the strip shapes respectively to the frame is also performed with high precision, the problem of displacement of the opening pattern in the other direction (the longitudinal direction) is not solved. Further, since the unit mask in the strip shape is constructed by a metal plate, the problem of positional displacements of the respective unit masking patterns due to distortion by the tare weights of the masks and the like, and the problem of difficulty in handling due to increase in the total mass including the frame are not thoroughly solved.